Chapter foci: –Chemical bonds and ion gradients are cellular energy –Membrane transport proteins...

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• Chapter foci:– Chemical bonds and ion gradients are cellular

energy– Membrane transport proteins play a role in energy

transduction– Energy transduction pathways in the chloroplast– Energy transduction in the mitochondria with an

emphasis on glucose metabolism– Energy transduction in bacteria are diverse

Chapter Summary: The Big Picture (1)

Chapter Summary: The Big Picture (2)• Section topics:

– Cells store energy in many forms– Gradients across cellular membranes are essential

for energy storage and conversion– Storage of light energy occurs in the chloroplast– Cells use a combination of channel, carrier, and

pump proteins to transport small molecules across membranes

– The first phase of glucose metabolism occurs in the cytosol

– Aerobic respiration results in the complete oxidation of glucose

Physiological status

Source of energy loss

Survival*Retainviability

Repair damage to key macromolecules

Maintenance*Sustain activity

Repair/replace of cellular materialMotilityInefficiency/heat generationFutile ion cyclingSecretion

Growth*Replication

All of the above, and:Replication of cellular material

logEsurvival: maintenance: growth 1:103:106

E: cellular energy supplyFs: substrate flux (FS), G'rxn: free energies for catabolism G'ATP: free energy for ATP synthesis

ADP + Pi = ATP (60 kJ mol-1) -n: translocated H+ for ATP synthesisE < ME= inactivity or death ME: maintenance energy

1-4 =100% efficient

Cells store energy in many forms

• Key Concepts (1):– Energy exists in three forms: kinetic, potential, and

heat.– The laws of thermodynamics define the rules for

energy transfer.– Cells remain alive by converting environmental

energy sources into cell-accessible energy forms.– High-energy electrons and ion gradients are the

most common forms of cellular energy storage.– The amount of energy in an ion gradient is

expressed as an electrical potential.

• Key Concepts (1):– Cells remain alive by converting environmental

energy sources into cell-accessible energy forms.

CO2 H2O

• Key Concepts (1):

*High-energy electrons

and ion gradients are the

most common forms of

cellular energy storage.

*The amount of energy

in an ion gradient is

expressed as an

electrical potential.

The laws of thermodynamics define the rules for energy transfer

• H2S released through volcanic activity

• H2S dissolves in H2O and reacts with metals to form precipitates

• 2 S-2 + Fe+2 FeS2 (pyrite)• SO2

-2 + Ca+2 CaSO4 (gypsum)

Fats and polysaccharides are examples of long-term energy storage

in cells

High-energy electrons and ion gradients are examples of short-term

potential energy

How cells store potential energy with gradients

• Cells couple energetically favorable and unfavorable reactions

• Nucleotide triphosphates store energy for immediate use

• The amount of potential energy stored in an ion gradient can be expressed as an electrical potential

ATP + H2O =ADP + Pi DGo’ =-30.5KJ/mole

ADP + H2O= AMP + Pi DGo’ = -28.4KJ/mole

Gradients across cellular membranes are essential for energy storage and

conversion • Key Concepts:

– Membrane transport proteins are responsible for moving ions through the phsopholipid bilayer of cellular membranes.

– Membrane transport proteins are organized into three groups: channels, carriers, and pumps.

– All channels dissipate gradients, all pumps build gradients, and most carriers only dissipate gradients. Some carriers can build gradients as well, using indirect active transport.

Phospholipid bilayers are semi-permeable barriers

Figure 10.01: Permeation of lipid bilayers by biologically important molecules.

Protein channels, carriers, and pumps regulate transport of small

molecules across membranes

• Protein channels dissipate gradients

Figure 10.02: Different views of a Cl- transporter. Note how several transmembrane alpha helices combine to form the

pore, including the selectivity filter.

Channel types

Ligand-gated Voltage-gated

Figure 10.03: Three methods for controlling the opening and closing of channels. Ca+2

channels are used as examples.

Figure 10.04: Three models for how voltage across a membrane controls the

shape of voltage-gated channels. Different types of K+ channels are shown

as examples.

Passive carrier proteins dissipate gradients

Figure 10.05: A comparison of channel and carrier proteins.

Figure 10.06: An example of a conformation change in a carrier

protein.

Symport and Antiport

Figure 10.07: Some examples of Na+-dependent transporters.

Energy-coupled carrier proteins (pumps) build gradients

Direct active transport Indirect active transport

Figure 10.08: The relationship between direct and indirect active

transport.

PUMPS, CHANNELS AND TRANSPORTERS

Transporters

Primary active transport:Transport depends on the energy from the hydrolysis of ATP

Membrane Transporter Proteins: Classification

Secondary active transport:Use of energy from a secondary diffusion gradient set up across the membrane using another ion. Because this secondary diffusion gradient initially established using an ion pump, as in primary active transport, the energy is ultimately derived from the same source-ATP hydrolysis.

Membrane Transporter Proteins: Classification

Facilitated diffusion:Transport from higher concentration to lower concentration. It does not require the expenditure of metabolic energy

Channels Selective transport water or ions down their concentration or electric potential gradients

Highly regulated

Energetically favorable reaction

A passageway across the membrane through which multiple water molecules or ions move simultaneously at a very rapid rate—up to 108 per second

Transporters: Uniporters

Transport is specific and saturable

Facilitated “low resistance” diffusion:

Down the concentration gradient

Reversible

Rate much higher than passive diffusion

Transporters:Secondary transporters

Couple the movement of one type of ion or

molecule against its concentration gradient to

the movement of a different ion or molecule

down its concentration gradient

Mediate coupled reactions in which an

energetically unfavorable reaction coupled to

energetically favorable reaction

Transporters:Secondary transporters

Catalyze “uphill” movement of certain molecules

often referred to as “active transporters”, but

unlike pumps, do not hydrolyze ATP (or any

other molecule) during transport

P, F, and V classes transport ions only, whereas the ABC superfamily class transports small molecules as well as ions.

Use the energy of ATP hydrolysis to move ions or small molecules across a membrane against a chemical concentration gradient or electric potential.

Overall reaction—ATP hydrolysis and the “uphill” movement of ions or small molecules—is energetically favorable

Storage of light energy occurs in the chloroplast

• Key Concepts (1):– Chloroplasts capture kinetic energy in photons of

sunlight and convert it into an ion gradient and high energy electrons, which are stored on the electron carrier NADPH.

– The machinery that converts sunlight into these energy forms is a cluster of proteins in the thylakoid membrane inside chloroplasts. Collectively, they are known as the thylakoid electron transport chain.

Storage of light energy occurs in the chloroplast

• Key Concepts (2):– The ion gradient energy is converted into ATP by

an enzyme called ATP synthase. – The energy in ATP and NADPH is used to

convert atmospheric CO2 into carbon-containing macromolecule called glyceraldehydes 3-phosphate via set of chemical reactions called the Calvin cycle.

Chloroplasts have three membrane-bound compartments

Chloroplasts convert sunlight into the first forms of cellular energy

• Light reactions - energy transduction reactions• Dark reactions - carbon assimilation reactions

The energy transduction (light) reactions convert sunlight into stored potential energy

The electron transport chain in the thylakoid membrane.

The “Z” scheme

The carbon assimilation (dark) reactions convert stored potential

energy into macromolecules

Figure 10.13: An overview of the Calvin cycle. Figure 10.14: The synthesis of

glucose and sucrose from G3P in the cytosol.

The carbon assimilation (dark) reactions convert stored potential

energy into macromolecules

The synthesis of glucose and sucrose from G3P in the cytosol.

• Key Concepts:– The majority of the macromolecules made by cells

can serve as food energy for other cells. To access this energy, the chemical bonds holding these macromolecules must be broken.

– In animals, macromolecules are broken into cellular building blocks (via digestion) in the extracellular space.

– Cellular building blocks (e.g., glucose) are transported across the plasma membrane by an integrated system of channels, carriers, and pumps.

Cells use combination of channel, carrier, and pump proteins to transport small molecules

across membranes

Macromolecule Transport

leaky K+ channel,

Na+/glucose symporter, and passive glucose carrier work together to move glucose from gut lumen to bloodstream

1.Cholera toxin subunit A crossesthe membrane and activates a G protein

The cholera toxin: when things go wrong with membrane function

cholera toxin Lumen

CytosolG protein

2. G protein activates adenyl cyclase to produce cAMP

CytosolACGs

Cytosol Cl- Na+

3. cAMP activates a Cl- channel.K+, Na+ Cl- and HCO3

- are secreted to theintestinal lumen. The lumen osmotic pressures rises

Cytosol Cl- Na+

HCO3- water

4. A large osmotic pressure gradientis established between the cytosol andthe lumen causing large amounts of water to go to the lumen. This produces diarrhea and dehydration

Cytosol

Water flow

5. :The Na+/glucose symporter binds Na+ and glucose in the lumen and transports both to the cytosol. This increases the osmotic pressure in the cell making water return to cell by osmosis

Cytosol

glucose

Na+/glucosesymporter

Oral rehydration: Gatorade

• Key Concepts (1):– The steps taken to extract energy from glucose

are very similar to the steps chloroplasts use to build glucose from G3P, only in reverse order.

– The first 10 enzymatic steps in the digestion of glucose are called glycoslysis.

The first phase of glucose metabolism occurs in the cytosol

• Key Concepts (2):– The products of glycolysis include the molecule

pyruvate, which must be metabolized to keep glycolysis from stalling.

– In the absence of molecular oxygen (O2), pyruvate is metabolized by a process called fermentation. Two different methods of fermentation have evolved in different organisms.

The first phase of glucose metabolism occurs in the cytosol

Glycolysis is subdivided into 3 stages

• The 10 chemical reactions in glycolysis convert glucose into 2-three-carbon compounds (pyruvate), two NADH molecules, and two ATP molecules

In the absence of O2, pyruvate undergoes fermentation

Figure 10.18: Three fates of pyruvate.

In the absence of O2, pyruvate undergoes fermentation

Figure 10.18: Three fates of pyruvate.

• Key Concepts (1):– The appearance of molecular oxygen in the

atmosphere allowed some organisms to harness the strong electronegativity of oxygen atoms to extract 18-fold more ATP energy than glycolysis alone.

– Aerobic respiration takes place in mitochondria, and occurs in four stages.

– Stage one converts pyruvate into acetyl CoA, the substrate of a metabolic cycle called the Krebs cycle (stage two).

– The Krebs cycle resembles the Calvin cycle run in reverse.

Aerobic respiration results in the complete oxidation of glucose

• Key Concepts (2):

5) During stage three, the high-energy electrons removed from pyruvate and acetyl CoA are passed through an electron transport chain in inner mitochondrial membrane, similar to thylakoids. At the end of the electron transport chain, the electrons are returned to oxygen atom to rebuild the water molecule that was oxidized at the beginning of photosynthesis, thereby completing the cyclic journey of electrons.

6) In stage four, the proton gradient formed by the electron transport chain is converted into ATP by and ATP synthase.

Aerobic respiration results in the complete oxidation of glucose

Aerobic respiration occurs in 4 stages (1)

• Stage 1: Pyruvate is transported into mitochondrial matrix and converted into acetyl CoA

• Stage 2: Acetyl CoA is fully oxidized to CO2, GTP, and high-energy electron carriers

Overview of mitochondrial respiration

Yield of the glycolysis-aerobic metabolism pathway

• Stage 3: The electron transport chain (ETC) uses high-energy electrons from NADH and FADH2 to build a proton gradient across the inner mitochondrial membrane

• Stage 4: The F1/Fo ATP synthase uses the proton gradient to make ATP

Figure 10.21: The mitochondrial electron transport chain.

The redox potential of reactants indicates the energy level of the electrons moving through the mitochondrial

electron transport chain.

A model of the F1Fo ATPase.

Final accounting of the ATP yield from aerobic metabolism

Chapter foci: –Chemical bonds and ion gradients are cellular energy –Membrane transport proteins...

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